The present invention relates to a silicone rubber adhesive film and to methods for adhering metal substrates to glass substrates.
Silicone rubber adhesive films are known. For example, Japanese Official Patent Publication (Kokoku) Heisei 7-119394 discloses a silicone rubber adhesive film prepared from an organopolysiloxane rubber and a wet method hydrophobized reinforcing silica with a curing accelerator. The silicone rubber adhesive film is simple to handle, possesses excellent workability, and is suitable for firmly securing together plates which have smooth surfaces and are made of such materials as glass, metal, etc. Furthermore, since the silicone rubber adhesive film can fix together glass and metal plates, it can be advantageously used as an adhesive for attaching knobs to glass entrance doors or to glass windows for buildings, for attaching mirrors (so called inner mirrors) to automobile windshield, etc. However, the adhesive strength of the silicone rubber adhesive film depends on the degree of its curing, and therefore there may be significant variations in the strength of the connections between structural elements secured with the use of this adhesive.
It is an object of the present invention to provide a colored silicone rubber adhesive film which is easily handled, possesses excellent workability, and most important, makes it possible to verify the degree and the point of completion of the curing in the silicone rubber adhesive film. When the latter is used for bonding various substrates together, it produces adhesive connections with improved uniformity.
Another object of the present invention is to provide methods for adhering metals substrates to glass substrates with the use of the colored silicone rubber adhesive film.
As a results of careful studies aimed at the solution of the problems described above, the present inventors have found certain organic pigments when present in a specific transparent silicone rubber adhesive film creates a colored film. The colored silicone rubber film become colorless upon subsequent heating and curing. This feature is used to verify the degree of curing, so that the moment at which the adhesive becomes completely colorless, curing completion is indicated. Furthermore, the inventors have discovered that the colored silicone rubber adhesive film produces bonded structures with improved uniformity in adhesive strength.